Li Liang, Low Jonathan Z, Wilhelm Jan, Liao Guanming, Gunasekaran Suman, Prindle Claudia R, Starr Rachel L, Golze Dorothea, Nuckolls Colin, Steigerwald Michael L, Evers Ferdinand, Campos Luis M, Yin Xiaodong, Venkataraman Latha
Department of Chemistry, Columbia University, New York, NY, USA.
Institute of Theoretical Physics, University of Regensburg, Regensburg, Germany.
Nat Chem. 2022 Sep;14(9):1061-1067. doi: 10.1038/s41557-022-00978-1. Epub 2022 Jul 7.
Single-molecule topological insulators are promising candidates as conducting wires over nanometre length scales. A key advantage is their ability to exhibit quasi-metallic transport, in contrast to conjugated molecular wires which typically exhibit a low conductance that decays as the wire length increases. Here, we study a family of oligophenylene-bridged bis(triarylamines) with tunable and stable mono- or di-radicaloid character. These wires can undergo one- and two-electron chemical oxidations to the corresponding mono-cation and di-cation, respectively. We show that the oxidized wires exhibit reversed conductance decay with increasing length, consistent with the expectation for Su-Schrieffer-Heeger-type one-dimensional topological insulators. The 2.6-nm-long di-cation reported here displays a conductance greater than 0.1G, where G is the conductance quantum, a factor of 5,400 greater than the neutral form. The observed conductance-length relationship is similar between the mono-cation and di-cation series. Density functional theory calculations elucidate how the frontier orbitals and delocalization of radicals facilitate the observed non-classical quasi-metallic behaviour.
单分子拓扑绝缘体有望成为纳米长度尺度上的导线。一个关键优势是它们能够展现准金属传输，这与共轭分子导线不同，共轭分子导线通常表现出低电导率，且随着导线长度增加而衰减。在此，我们研究了一族具有可调节且稳定的单自由基或双自由基特性的亚苯基桥连双（三芳基胺）。这些导线分别可以经历单电子和双电子化学氧化，生成相应的单阳离子和双阳离子。我们表明，氧化后的导线随着长度增加呈现出相反的电导率衰减，这与对Su-Schrieffer-Heeger型一维拓扑绝缘体的预期一致。此处报道的2.6纳米长的双阳离子显示出大于0.1G的电导率，其中G是电导量子，比中性形式大5400倍。单阳离子和双阳离子系列之间观察到的电导-长度关系相似。密度泛函理论计算阐明了前沿轨道和自由基的离域如何促进观察到 的非经典准金属行为。
